Halevy was the sole judge in what became known as the "Kastner trial," a libel lawsuit against Malchiel Gruenwald, a hotelier, who accused Rudolf Kastner of having been a Nazi collaborator. Halevy allowed the scope of the trial to be expanded and ruled that Kastner had indeed, in his words, "sold his soul to the devil." Kastner was later assassinated and Halevy's ruling was mostly overturned by the Supreme Court. The manner in which he conducted the trial was criticized.

Halevy was the sole judge at the trial of the Kafr Qasim massacre's perpetrators, and in his decision famously wrote, "The distinguishing mark of a manifestly illegal order is that above such an order should fly, like a black flag, a warning saying: 'Prohibited!'" He was later a judge at the trial of Adolf Eichmann, along with Yitzhak Raveh and Moshe Landau.

In 1969 Halevy resigned from the court in order to enter politics. He was elected to the Seventh Knesset for the Gahal (Herut-Liberal Bloc) list, and again to the Eighth Knesset in 1973 after Gahal had merged into Likud. He later left the party to sit as an independent MK. In the 1977 elections, he was returned to the Knesset on Dash's list, but the party split up after a year, and Halevy joined the Democratic Movement, before leaving to again sit as an independent. During the Ninth Knesset he also served as deputy speaker.

Today a street in his birthplace Weißenfels is named after him.

He was married for many years to Luba. They had a son and daughter. After Luba's death he married Michal Halevy.